Our Glide-On Cassette® balcony system is an approved product detail by Premier Guarantee.
View the Premier Guarantee Approved Products here.
The National House Building Council (NHBC) sets building standards and provides warranty and insurance for new homes. They work with housing developers to comply with their 10-year Buildmark policy, which currently covers over 75% of new homes and protects around 1.5 million homes around the UK.
NHBC Key Points
See NHBC Standards, chapters 7.1 & 7.2
- Balconies over 6m² must be drained to a RWP or edge drained
- Open Balconies should be drained away from the home
- Water management should be considered for all balconies
- Door sills to project min 45mm
- Door thresholds upstand to be 15mm max
- Guarding to be a minimum of 1100mm high.
What is the NHBC?
NHBC is the UK’s leading independent standard-setting body and provider of warranty and insurance for new homes. They work with the majority of sizeable developers and on most substantial developments. There are other warranty providers like Premier Guarantee however unlike NHBC most others don’t insist on additional standards of their own.
How do NHBC requirements affect balcony design?
The NHBC standards are led by years of knowledge built from the issues which cause insurance claims. With balconies, this mainly affects rainwater management and details around junction points.
It is important to note that NHBC guidance, prior to the launch of the NHBC 2016 Standards Plus, was set out in self-contained sections of key topics. There is now just one set of standards which combine the guides into chapters within the main standards. However, some guidance has been withdrawn and replaced, which in terms of balconies, has clarified some points of confusion.
The guidance is written in the NHBC 2021 Standards Plus – which updated several chapter 7 sections from the 2016 version. Both clarify the areas developers need to focus on. The risk guide on balconies covers five main areas: structure, drainage, waterproofing, accessible threshold and guarding.
Key Considerations for NHBC Compliance
- Timber supports are prohibited from being used in the balcony structure as supports for decking, regardless of the height of the building.
- In-situ reinforced concrete decks should be formed using a mix which has low shrinkage characteristics. They should have accurately constructed and suitably supported formwork and be protected until adequately cured and dried.
- Precast concrete decks should be installed on an even and true supporting structure. They must have a minimum 90mm bearing (unless design states otherwise), have allowance for continuity or anti-crack reinforcement and have allowance for movement approximately every 15 metres and at abutments.
- Structural elements are required to have a service life of at least 60 years.
- Profile metal decks should be constructed in accordance with manufacturer’s recommendations to achieve required strength and durability.
- The principles for drainage given in chapter 7.2 ‘pitched roofs’ [in particular, areas over 6m²] are applicable to flat roofs. Other areas, such as balconies, should be considered.
- Rainwater disposal from roofs and balconies 6m² or less in area should be considered. Edge drainage is considered a solution in this area.
- When run-off may cause damage or staining to a façade or damage to landscaping, then rainwater gutters and downpipes should be provided.
- If there is potentially a cumulative effect of water discharging from multiple balconies in vertical alignment, this should be taken into account with the drainage method.
- Open balconies should drain away from the home.
- Decking gaps should be provided between decking and paving at balcony perimeters. At least 10mm gaps should be provided between individual units of decking or paving and the threshold sill perimeter walls and kerbs. The spacers and supports which raise decking or paving should not obstruct the flow of rainwater to outlets.
- Waterproofing concrete balconies
- Waterproofing systems should be laid according to the design, specification and manufacturer’s recommendations.
- Membranes should not be laid on damp or frosted surfaces or when any rain, sleet or snow is falling. They should not be laid or handled when the air temperature is 5°C or lower.
- Once completed, the waterproof membrane should be visually inspected and electronically tested for integrity.
- The tested membrane should be protected from damage until subsequent layers are applied.
- Accessible threshold
- Thresholds much be in accordance with the design – specific fire, thermal and acoustic precautions may be required.
- There must be a maximum 15mm upstand (measured at the door position) at the door threshold.
- Additional sloping transition elements, such as a small internal ramp and external sill, may be provided to either side of the upstand. The maximum slope on ramps and sills should be 15 degrees.
- A minimum 45mm projecting sill is required to shed rainwater away from the interface with the waterproofing layer.
- There should be a 75mm minimum balcony upstand below the underside of the projecting sill, measured from the balcony drainage layer.
- Guard rails and barriers must be a minimum of 1100mm high.
- They should not be readily climbable by children or allow a 100mm diameter sphere to pass through them.
NHBC Standards on Balconies
7.1 Defines balconies into 6 categories:
- Projecting – cantilevered from the external wall line of a building.
- Inset – recessed inwards from the external wall line of a building.
- Open – has guarding but no other form of vertical enclosure
- Enclosed – protected from rain by a roof or balcony above and walls or weather screens to the
sides, (sometimes referred to as a ‘winter garden’).
- Access balcony – Providing pedestrian access to two or more dwellings. (Sometimes referred
to as a ‘walkway’ or ‘access deck’).
- Freestanding – fully, or partially, supported independent of the building structure.
7.1.5 (Drainage) states that “Flat roofs, balconies and terraces shall have adequate and effective rainwater drainage to a suitable outfall.” Also that “A drainage system of outlets and downpipes should be provided to all flat roof, balcony and terrace areas.”
It further states: “Balconies and terraces which project no more than 2.5m from the face of the building may be drained over a perimeter edge into open space provided the run-off does not cause damage or staining to surfaces below, or damage or erosion to landscaping, or nuisance to people using or visiting the building. The drained edge should start at least 400mm away from an adjacent wall and be at least 25mm below any spill over level into the building e.g. underside of any door thresholds into the building. Concentrations of edge flow should be avoided, and water should be dispersed as evenly as practicable. Edge drainage should not be adopted over private gardens, streets, public pathways or over building entrances unless a suitable canopy or alternate protection is provided. The collecting surface should have no other surfaces relying upon it for drainage. The edge drainage should project and turn down to form a drip edge at least 30mm beyond the adjacent vertical surface.”Further detail on 7.1.5.
7.1.6 (Flat roof, terrace and balcony structural design) states the structure of a balcony should “be designed to address both short term and long-term deflection to provide an effective drainage strategy with no back falls or ponding.”
7.1.17 (Accessible thresholds) states thresholds should:
- Have a minimum 45mm projecting sill to shed rainwater away from the interface with the waterproofing layer with a drip feature a minimum 30mm away from the face of the upstand.
- Have a 75mm minimum balcony upstand below the underside of the projecting sill, measured from the balcony/ terrace drainage layer.
7.1.18 (Parapets and guarding to terraces and balconies) states guarding should:
- not be easily climbed by young children
- be to an adequate height
- be toughened glass, laminated glass (subject to meeting fire regulations) or glass blocks (suitably reinforced) where glazed balustrading is used
- not inhibit the flow of drainage on the waterproofing layers or overflows in the event of a blocked outlet
It also recommends that all guarding is designed in accordance with BS EN 1991-1-1 to resist horizontal loadings and as required by building regulations. They recommend that in balcony walls the structural stability is checked as cavity trays can DPCs in the wall can create a slip place which may limit the ability of the wall to resist horizontal forces.
7.2.22 (Drainage) This section is subtitled with a statement that ‘roof drainage shall adequately carry away rainwater to suitable outlet’.
The key guidance from this sections states that ‘drainage should be provided where roofs are greater than 6m²; however, consideration should be given to providing drainage to smaller roofs such as dormer, porch roofs and balconies (see Clause 7.1.12)”.
Our understanding is that these points clearly indicate that the NHBC expect balconies over 6m² to have rainwater drainage (positive drained balconies) and that in some cases water will be discharged into the open, not into a RWP.
The NHBC has clarified to Sapphire that “just because [balconies] may be less than 6sq m doesn’t mean to say that the water should not be managed, because this may lead to flooding/waterlogging within 3m of the property”. If balconies are free drained to the front rather than to spouts it is less likely to cause concentrated puddling or waterlogging at ground level.
A stack of balconies can be considered somewhat like a tree; when it starts to rain, the balconies (like leaves and branches) trap and collect water. For a while, you would be less wet standing underneath than if you were standing in the open. However, if rain persists, water will start to drip in some places in an uneven pattern. Once the rain has ceased, water will continue to drip for a while, like it does from a tree.
Taking water from projecting balconies inside the building envelope to a RWP (Rain Water Pipe) generates the risk of water ingress if anything goes wrong or gets blocked. Some clients believe drainage to a drip edge is, therefore, a more satisfactory long term solution than draining to a RWP.
As some of the guidance is not definitive, particularly in relation to how balconies are to be drained, Sapphire strongly recommends that NHBC inspectors are consulted in the early stages of a project to ensure proposed solutions meet their approval.
Drainage requirements have always been a client decision, but in supplying balconies for many residential projects we have found that:
20% of clients have chosen positive drainage to a RWP
75% of clients have chosen positive draining to a drip edge or spout
5% of clients have chosen free drainage with no soffit
There seems to be a distinct growing trend of moving away from balconies without soffits. A trend which Sapphire is completely in support of.